Network Working Group M. Nottingham
Internet-Draft E. Hammer-Lahav
Intended status: Informational September 17, 2009
Expires: March 21, 2010
Defining Well-Known URIsdraft-nottingham-site-meta-03
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Abstract
This memo defines a path prefix for "well-known locations" in URIs.
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Internet-Draft Defining Well-Known URIs September 20091. Introduction
It is increasingly common for Web-based protocols to require the
discovery of policy or metadata before making a request. For
example, the Robots Exclusion Protocol specifies a way for automated
processes to obtain permission to access resources; likewise, the
Platform for Privacy Preferences [W3C.REC-P3P-20020416] tells user-
agents how to discover privacy policy beforehand.
While there are several ways to access per-resource metadata (e.g.,
HTTP headers, WebDAV's PROPFIND [RFC4918]), the perceived overhead
associated with them often precludes their use in these scenarios.
When this happens, it is common to designate a "well-known location"
for such metadata, so that it can be easily located. However, this
approach has the drawback of risking collisions, both with other such
designated "well-known locations" and with pre-existing resources.
To address this, this memo defines a path prefix for these "well-
known locations", "/.well-known/". Future specifications that need
to define a resource for such site-wide metadata can register their
use to avoid collisions and minimise impingement upon sites' URI
space.
Please discuss this draft on the apps-discuss@ietf.org [1] mailing
list.
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Well-Known URIs
A well-known URI is a URI [RFC3986] whose path component begins with
the characters "/.well-known/".
Applications that wish to mint new well-known URIs MUST register
them, following the procedures in Section 5.1.
For example, if an application registers the value 'example', the
corresponding well-known URI on 'http://www.example.com/' would be
'http://www.example.com/.well-known/example'.
Note that this specification defines neither how to determine the
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Internet-Draft Defining Well-Known URIs September 2009
authority to use for a particular context, nor the scope of the
metadata discovered by dereferencing the well-known URI; both should
be defined by the application itself.
Typically, a registration will reference a specification that defines
the format and associated media type to be obtained by dereferencing
the well-known URI.
It MAY also contain additional information, such as the syntax of
additional path components, query strings and/or fragment identifiers
to be appended to the well-known URI, or protocol-specific details
(e.g., HTTP [RFC2616] method handling).
Note that this specification also does not define a format or media-
type for the resource at located at "/.well-known/" and clients
should not expect a resource to exist at that location.
4. Security Considerations
This memo does not specify the scope of applicability of metadata or
policy obtained from a well-known URI, and does not specify how to
discover a well-known URI for a particular application. Individual
applications using this mechanism must define both aspects.
An attacker with certain types of limited access to a server may be
able to affect how well-known URIs are served; for example, they may
be able to upload a file at that location, or they may be able to
cause a server to redirect a well-known URI to a URI that they
control.
Because most URI schemes rely on DNS to resolve names, they are
vulnerable to "DNS rebinding" attacks, whereby a request can be
directed to a server under the control of an attacker.
5. IANA Considerations5.1. The Well-Known URI Registry
This document establishes the well-known URI registry as the name
space of URIs that have a path beginning with "/.well-known/".
Well-known URIs are registered on the advice of a Designated Expert
(appointed by the IESG or their delegate), with a Specification
Required (using terminology from [RFC5226]).
Registration requests consist of the completed registration template
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Internet-Draft Defining Well-Known URIs September 2009
(see Section 5.1.1), typically published in an RFC or Open Standard
(in the sense described by [RFC2026], section 7). However, to allow
for the allocation of values prior to publication, the Designated
Expert may approve registration once they are satisfied that an RFC
(or other Open Standard) will be published.
Upon receiving a registration request (usually via IANA), the
Designated Expert should request review and comment from the apps-
discuss mailing list (or a successor designated by the APPS Area
Directors). Before a period of 30 days has passed, the Designated
Expert will either approve or deny the registration request,
communicating this decision both to the review list and to IANA.
Denials should include an explanation and, if applicable, suggestions
as to how to make the request successful.
5.1.1. Registration Template
URI suffix: The name requested for the well-known URI, relative to
"/.well-known/"; e.g., "example". MUST conform to the segment-nz
production in [RFC3986].
Change controller: For standards-track RFCs, state "IETF". For
other open standards, give the name of the publishing body (e.g.,
ANSI, ISO, ITU, W3C, etc.). A postal address, home page URI,
telephone and fax numbers may also be included.
Specification document(s): Reference to document that specifies the
field, preferably including a URI that can be used to retrieve a
copy of the document. An indication of the relevant sections may
also be included, but is not required.
Related information: Optionally, citations to additional documents
containing further relevant information.
6. References6.1. Normative References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
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